The present invention relates to heating or cooking apparatus in which heated air is forceably circulated in order to provide efficient and even heating of the material being heated within a heating compartment. Apparatus of this type are referred to in the trade as "convection ovens". More particularly, the forced air apparatus of the present invention establishes increased flexibility by providing means to generate and use both a directly heated air stream and a recirculated air flow both within the oven. The heated air stream also provides indirect heat transfer into the oven.
Ovens showing forced air recirculating impeller fans are set forth in U.S. Pat. Nos. 3,118,436 to R. T. Keating, 3,148,674 to R. T. Boardman et al, and 3,411,493 to G. R. Everson et al. Each of these patents show an oven compartment in which air is forceably recirculated by an impeller fan located in the rear portion thereof. Each of these ovens is provided with a gas combustion heating means for heating the main oven compartment.
Some of the prior art has specified that the heating compartment should have a particular exterior configuration with respect to the flow patterns established by the impeller fan such as U.S. Pat. No. 3,463,138 to Lotter et al. Yet other prior art of this type has provided for various cooling channels in order to cool the impeller motor as in U.S. Pat. No. 3,707,145 to Anetsberger et al.
Other prior art provides for flow-through of the heated air rather than recirculation of the air within the oven heating compartment. Representative patents of this type which have fan means for drawing the heated air through the heating compartment are: U.S. Pat. Nos. 3,437,085 to Perry; 3,973,551 to Caselani et al; and 4,108,139 to Gilliom et al. The fan means in these patents provide for movement of heated air through the oven compartment in order to heat the material being cooked or treated within the oven. The air flow patterns established in these patents provide for the contacting of hot combustion gases with an air stream which is drawn through the oven compartment walls. The contact between the combustion gases and the air stream drawn through the oven compartment occurs outside of the oven compartment. After the mixing of the flow-through oven air with the combustion gases the combined air stream is redirected through the oven heating compartment walls. These oven apparatuses do not provide for the continual recirculation of air within the heated chamber by a fan placed therein but rather require a flow-through of heated air. In these ovens there is no provision for controlling the relative proportions of the hot combustion gases and the heated air stream flowing through the oven compartment.
A problem encountered in these flow-through type ovens with food broiling and roasting is that the air flow stream exiting from the heating compartment contains various organic matter given off by the food as it is heated, particularly grease. This matter can then deposit on the air conduit surfaces and constitutes operational and safety hazards.
Other patents provide for recirculation of heated air in an oven compartment as well as a ventilating flow of air through other portions of cooking ranges in which the oven compartments are placed. Representative patents of this type are U.S. Pat. Nos. 4,071,738 and 4,071,739 both to Jenn et al. Another patent not showing recirculated air within the oven compartment but providing for ventilating air flow is U.S. Pat. No. 3,587,555 to Cerola.
The above-referred-to patents do not show the primary heating of air at one remote location within the oven apparatus, circulation of the heated air to the oven compartment through conduit(s) which enable indirect heating of the oven compartment, and contacting of the heated air stream with recirculated air within the heating compartment in order to form a dual primary heated air/recirculated air flow within the heating compartment. These patents do not simultaneously provide for the direct introduction of heated air into the heating compartment and recirculation within the compartment whereby matter given off by the heated food is confined to the heating compartment and the vent conduit(s) downstream from the heating compartment. The prior art also does not show a dual function impeller fan for providing the motive force for moving both the heated air stream and the recirculated heating compartment air flow which also functions as a mixing fan so that only a single motor can be used for the dual functions.